Eccentric crank linkage



March 24, 1953 G, s, P s 2,632,421

' VECCENTRIC CRANK LINKAGE Filed D60. 11, 1945 INVENTOR GERALD S. PERKINS ATTORNEY.

Patented Mar. 24, 1953 UNITED STATES gram" OFFICE ECCENTRIC CRANK LINKAGE Navy Application December 11, 1945, Serial No. 634,299

4: Claims.

This invention relates to an eccentric crank linkage, and more particularly to such a linkage adaptable to use for expanding an indicator dial reading about its zero point.

In some indicator applications, it is desirable to convert linear shaft rotation to a non-linear indication on a center-zero scale, with the nonlinearity resulting in greatest expansion around the Zero point. An example of this is a navigational left-right or yaw indicator, showing a ships heading relative to its desired course.

Accordingly, one object of this invention is to provide a center-zero indicator with an expanded scale about the zero point.

Another object is to provide an expanded center-zero scale indicator with no limits of operation in that continuous rotation of the dial pointer in either direction is possible.

Another object is to provide a means for converting a linear shaft rotation into a non-linear rotation.

Still another object is to provide an eccentric crank linkage to expand a center-zero indicator dial reading about its zero point.

Other and further objects will appear durin the course of the following description when taken with the accompanying drawings in which:

Fig. 1 shows a front view of a navigational left-right or yaw indicator utilizing one embodiment of this invention;

Fig. 2 shows a generally cross-sectional View through center lines II-'II of Figs. 1 and 3; and

Fig. 3 shows a back view of the indicator shown inFig. 1.

In Fig. 1 the front view of the yaw indicator shows a housing I I enclosing circular dial l 2 and indicator needle l3 pivoted at one end. As illustrated, the dial scale units are expanded about the zero point of the center-zero scale.

Fig. 2 shows in detail the mechanism by which this expansion about the zero point is obtained. One arm of an L-shaped rod l5 extends through the center of housing H and has secured to its end needle I 3, as by a machine screw [6. The central portion of housing II is enlarged into a hub, as at ll, around the hole through which rod l5 extends to provide a larger bearing surface. The other arm of rod 55 is slidably attached to guide I B, which guide is attached to an arm I9 by machine screw 20. Only the portion of screw 20 which fits into guide I8 is threaded, so the hole in arm I9 through Which screw 20 extends provides a bearing surface. Screw 2B and this hearing surface thus provide a rotating joint. The other end of arm I9 is drilled to receive rotatable 2 shaft 2!, to which it is rigidly fastened by any suitable means.

Fig. 3 shows in another view the way in which the component parts are disposed. As shaft 2| connected to the desired control mechanism rotates in either direction, arm l9 rotates in the same direction through the same angle, carrying with it guide 18. Guide [8 slides along rod l5, causing rod I5 to rotate in hub I! through a greater angle than shaft 2! turns, and since needle [3 is rigidly secured to the end of rod l5, it rotates through the same greater angle. The ratio of the angle turned by rod l5 and needle [3 relative to the angle turned by shaft 2| is controlled by the distance a,'shown in Fig. 2, between the center lines of shaft 2| and the portion of rod l5 disposed parallel to shaft 2! The greater the distance a, the greater this ratio will be. It will be noted that shaft 2| can be rotated in either direction continuously and the mechanism will follow, and also that the greatest expansion of the dial scale occurs about the zero point. In addition, if it is desirable to indicate a complete reversal of direction, from mechanical considerations of the mechanism it can be seen that the 180 degree position of needle l3 and shaft l5 corresponds exactly to the 180 degree position of shaft 2!, in spite of the expansion elsewhere on the dial scale.

While a particular embodiment of this invention has been described as required bythe patent statutes, the principles of this invention are broader in ways which will be apparent to those skilled in the art. The scope of the invention is defined in the following claims.

What is claimed is:

1. Apparatus for indicating. comparatively small angular displacements of a rotatable shaft from a predetermined position comprising an indicating needle, an indicating dial having calibrated markings thereon and a substantially central bearing, an L-shaped rod having one arm thereof rotatably disposed within and extending through said bearing, said indicating needle being rigidly attached to the end of said arm extending through said bearing and being operable over the face of said dial in proximate relation with said calibrated markings, a guide slidably fitted over the other arm of said L-shaped rod, and a member pivotally attached at one end thereof to said guide for rotation about an axis normal to said last-mentioned arm and rigidly secured at its other end to said rotatable shaft, said member extending radially of said rotatable shaft,

' the axis of said dial bearing being disposed parallel to and offset from the axis of said rotatable shaft, whereby for a comparatively small angular range of rotation about said predetermined position, the indicating needle angular rotation is substantially greater than the shaft angular rotation, said indicating dial markings being calibrated in terms of the angular rotation of said shaft.

2. Apparatus for transmitting angular motion from a rotatable shaft comprising, an L-shaped rod having a first arm journaled for rotation about an axis parallel to and offset from the axis of said rotatable shaft, a member rigidly secured to and extending perpendicularly from said rotatable shaft, and a guide formed with a bore therein slidably fitted upon the second arm of said L-shaped rod, said guide being supported upon said member for rotation about an axis parallel to said rotatable shaft.

3. Apparatus as in claim 2 and including a dial having markings thereon, said dial being fitted over said first arm, and an indicating needle attached to the end of said first arm and operable over the face of said dial in proximate relation with said markings.

4. Apparatus for indicating the angular displacement of a rotatable shaft from a predetermined position comprising, a scale carrying structure having a bearing formed therein on an axis substantially parallel to and offset from said rotatable shaft, an L-shaped rod having one arm rotatably extending through said bearing, a link radially extending from said rotatable shaft and rigidly joined thereto, motion coupling means rotatably attached to said link and slidably fitted to the other arm of said L-shaped rod, said coupling means being oifset from both said rotatable shaft and said arm extending through said bearing, and indicating means secured to said arm extending through said bearing and operatively associated with said scale.

GERALD S. PERKINS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,115,000 Martin Oct. 27, 1914 1,810,355 Kingsford et a1. June 16, 1931 FOREIGN PATENTS Number Country Date 636,005 France Jan. 6, 1928 

